The present disclosure relates to an apparatus and method for automatically indicating when to change the engine lubricating oil by measuring the oil's viscosity. Traditionally, engine oil is changed whenever the vehicle reaches a predetermined mileage, or a specified time interval, which ever comes first. Under severe operating conditions, however, the vehicle manufacturers may suggest that the engine oil be changed more frequently.
These situations require the operator of the vehicle to make a judgment as to when to change the engine oil. This judgment is typically a guess, since the operator has no physical data on which to base the judgment. Typically, degradation of the engine oil occurs most rapidly at high and low temperature extremes. At high oil temperatures, antioxidants in the oil tend to become depleted, and the oil becomes more viscous and acidic due to oxidation. In addition, insoluble particles are deposited on the engine surfaces. At low oil temperatures, fuel, water and soot tend to accumulate in the oil, reducing its viscosity and increasing wear.
Uncertainty of when to change the engine oil may result in changing the engine oil more frequently than is necessary, which is a waste of money, or not changing the oil frequently enough, resulting in shortened engine life. “Good” oil has viscosity characteristics sufficient to give good hydrodynamic lubrication of the loaded surfaces, yet flows around the engine well enough to provide a continuous supply of fresh lubricant. Therefore, oil viscosity is a useful parameter for determining when the oil needs to be changed.